#include<string>
#include<vector>
#include<iostream>
using namespace std;
vector<string> v{ "" ," ","abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz" };
vector<string> num;
string ptm;
void Combinations(string digits, size_t x)
{
	if (x == digits.size())
	{
		num.push_back(ptm);
		return;
	}
	int y = digits[x] - '0';
	int size = v[y].size();
	for (size_t i = 0; i < size; i++)
	{
		ptm.push_back(v[y][i]);
		Combinations(digits, x + 1);
		ptm.pop_back();

	}
}

vector<string> letterCombinations(string digits) {
	if (digits.size() == 0)
	{
		return num;
	}
	Combinations(digits, 0);
	return num;
}
int main()
{
	letterCombinations("23");
	return 0;
}
